Metal halide perovskites nanocrystals (NCs) represent an emerging class of materials that find increasing application in optoelectronic and photovoltaic devices, thanks to their intriguing optical properties, including high absorption coefficient, high fluorescence quantum yield (PL QY) and fast charge carrier separation. However, their opening to market is still hindered by their limited reliability, due to an intrinsic structural instability and degradation of their photophysical properties upon air, moisture, and light exposure. The incorporation of perovskite NCs in polymer matrix can limit some of the NC instability issues, with advantages in film processability, device fabrication and mechanical performance, being also useful for fundamental studies. In this regard, here, nanocomposites based on polymethylmethacrylate or polystyrene embedding all-inorganic CsPbBr3 NCs have been prepared and processed in the form of flexible free-standing films. A systematic spectrofluorimetric study, comprising steady state photoluminescence (PL), PL quantum yield (QY) and PL decay of the free-standing films before and after exposure to relative humidity condition (RH% 85%, at 25 °C) is performed and discussed. Phase segregation phenomena, changes in NC passivation and recombination dynamics are evaluated as a function of polymer loading and its molecular structure and finally the efficacy of the polymer as moisture barrier investigated.